GEORG SIMON OHM 



1789-1834 



Ohm's law is to-day a commonplace for every technical 

 electrician. It is the means by which the strength of an 

 electric current can be calculated beforehand, when the 

 power of the source of current and the nature of the circuit 

 are known. When Volta had provided a plentiful source of 

 electric current, and Oersted the means for easily measuring 

 it, and Ampere had introduced a useful and definite con- 

 ception of current, one would have supposed that a need for 

 a knowledge of the way in which the current depends upon 

 the factors determining it would have been felt by the many 

 persons who now began to busy themselves with it. This 

 was far from what actually happened. Ohm in his time 

 announced his law to deaf ears, which shows us on the one 

 hand how superficial the requirements of the majority were, 

 and on the other hand how far in advance of his time Ohm 

 was as regards clear thinking. As a matter of fact, only 

 Davy and Ampere had approached near to the law before 

 his time. Both of them had already grasped, in the year 

 1 82 1, the idea of the resistance of a conductor, inasmuch as 

 they took note of the dependence of the current strength 

 upon the nature of the circuit, whereby Davy estimated the 

 strength of the current according to its chemical eff"ects, and 

 thus compared a number of diff^erent metals as conductors 

 with one another, determined the unessential effect of the 

 form of the cross-section by comparison of simple, multiple 

 and flattened wires, and also discovered the increase of 

 resistance of metals with temperature. 



It was Ohm who grasped the questions already illuminated 

 by these investigators, and pursued them in all directions to 

 complete solution. Using very poor and deficient apparatus, 

 he performed a series of decisive experiments, which 

 completely settled the question of the distribution of 



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